CHANMASTER - Chandra Observations

This database table contains all of the observations made by the Chandra
X-Ray Observatory (CXO, formerly known as the Advanced X-ray Astrophysics
Facility or AXAF) as part of the Performance Verification and Calibration
(PVC) phase and also contains all of the subsequent Cycles' Guaranteed Time
Observers (GTO) and General Observer (GO) targets, and any Director's
Discretionary Time (DDT) targets that have been observed. It also includes
scheduled and as-yet-not-scheduled targets.

The HEASARC updates this database table on a twice-weekly basis by querying
the database table at the Chandra X-Ray Center (CXC) website, as discussed in
the Provenance section. For observations whose status is 'archived', data
products can be retrieved from the HEASARC's mirror of the CXC's Chandra Data
Archive (CDA). The CXC should be acknowledged as the source of Chandra data.

The PVC phase was during the first few months of the CXO mission; some of the
calibration observations that are for monitoring purposes will be performed
in later mission cycles. All calibration data (entries with Type = CAL in
this database) are placed immediately into the CXO public data archive at the
Chandra X-Ray Observatory Center (CXC); please see the Web page at
http://asc.harvard.edu/ for more information on the CXC data archive). GTO
observations during Cycle 1 or any subsequent Cycle will probably occupy 100%
of months 3-4, 30% of months 5-22, and 15% of the available time for the
remainder of the mission. Guaranteed Time Observers will have the same
proprietary data rights as General Observers (i.e., their data will be placed
in the public CXC archive 12 months after they have received the data in
usable form).

Links to the HEASARC's mirror of the Chandra Data Archive (CDA) are also
accessible through the Browse Web interface for table entries where the
status is 'archived'. These links allow the user to select the Chandra data
products that are available in the CDA. These product categories include the
observation summary file, the V&V Report, images and source lists (both FITS
and JPEG), events lists, orbital ephemeris abd aspect solution files, gain
plots, spectra, bad pixel lists, and miscellaneous files. Using this method,
the TAR file is created on the fly, and data from multiple observations can
be retrieved together. The CXC should be acknowledged as the source of
all Chandra data.

Status
The current status of the observation and its associated dataset:
this is set to 'ARCHIVED' if the dataset is available to the public in
the CXC archive. The more-or-less self-explanatory values for the status
are 'UNOBSERVED', 'SCHEDULED', 'PARTIALLY OBSERVED', 'OBSERVED',
'DISCARDED', and 'ARCHIVED'. Observations with 'DISCARDED' status
are ones for which the Chandra Project considered that there were
no useful data.

Detector
The detector requested for the exposure. There are 2 focal-plane
scientific instruments, the AXAF CCD Imaging Spectrometer (ACIS) and the High
Resolution Camera (HRC). The ACIS has 2 arrays of CCDs: the ACIS imaging
array (ACIS-I) is optimized for imaging wide fields, while the ACIS
spectroscopic array (ACIS-S) is optimized for grating spectroscopy and for
imaging smaller fields. The HRC consists of 2 microchannel plate array which
are used as the primary detection devices: the HRC-I is optimized for direct
imaging, while the HRC-S is optimized for imaging the dispersed flux from the
Low Energy Transmission Grating (LETG). Thus, there are 4 possible detectors:
ACIS-I, ACIS-S, HRC-I, and HRC-S.

Grating
The grating setting requested/used for the exposure. There are two
objective transmission gratings: the High Energy Transmission Grating (HETG)
and the Low Energy Transmission Grating (LETG). The ACIS-S detector is normally
used to read out the HETG spectra, while the HRC-S detector is normally used
to read out the LETG spectra. Thus, there are 3 possible grating selections:
LETG, HETG, and NONE (i.e., no grating requested).

Exposure
The actual exposure time, in seconds, if the observation has been made. If
the observation has not been made yet, this is the approved exposure time, in
seconds. This parameter was given with a precision of 0.01 kiloseconds in the
original data file.

Type
The type of observation. There are five general types of target:
those accepted in a General Observer (GO) proposal (type = 'GO'), those
accepted in a Guaranteed Time Observing (GTO) proposal (type ='GTO'), those
used for a Calibration observation (type = 'CAL'), those accepted as Targets
of Opportunity (type = 'TOO'), and those observed as Director's Discretionary
Time (type = 'DDT'). Please note that some DDT targets may have been
designated as TOO targets.

PI
The last name of the assigned Principal Investigator (PI) for the
observation. Notice that this is not
always an unambiguous identifier, since there are a number of last names
(e.g., Drake and White) which are shared by more than one astronomer. If
in doubt, it is recommended that the target lists at
http://cxc.harvard.edu/target_lists/ be consulted for the full PI name for
all accepted proposals.

Cycle
The cycle number in which the proposal to observe the particular
target was submitted. Note that any observations which the CXC have not
assigned proposal numbers have been defaulted to a value of 0 for this
parameter in this HEASARC database.

Proposal
The proposal number to which the target corresponds as
assigned by the CXC.

Sequence_Number
The sequence number to which the observation corresponds
(assigned by the CXC).

Data_Mode
The operational (SI) mode of the detector. For ACIS it is of the form
Ty_xxxxx or
CC_xxxxx, where y is an uppercase letter and x is a hexadecimal digit; Ty
indicates timed exposure, CC continuous clocking. For HRC it will be DEFAULT
for most observations. More information on the ACIS SI modes is available at
CXC web site: http://asc.harvard.edu/acis/simode_query.html

Category
The subject category of the observation, as assigned by the CXC.

Class
The Browse Object Classification, as derived from the Category
parameter provided by the CXC. Note: This is done through a rather crude
mapping. Some of the assigned classes will be incorrect. E.g., observations
assigned to the isolated neutron stars and supernovae category will be mapped
to the supernova remnant Browse object class, since all three are grouped in
one Chandra category.